Centrifugal pump



Jan. 4, 1955 w. sTELzER CENTRIFUGAL PUMP 3 Sheets-Sheet l Filed Aug. 13, 1949 N. .WN

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Jan. 4, 1955 w. sTELzER 2,698,584

CENTRIFUGAL PUMP' Filed Aug. 13, 1949 3 Sheets-Sheet 2 1N VEN TUR.

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Jan.`4, 1955 w. sTELzER 2,698,584

CENTRIFUGAL PUMP Filed Aug. 13, 1949 (5 Sheets-Sheet 5 IN VEN TOR.

United States Patent CENTRIFUGAL PUD/IP William Stelzer, Summit,N.-J.

Application August 13, 1949, Serial No. 110,166

8 Claims. (Cl. Il3-I11)'.

The invention relates to centrifugal pumps and more particularly to novel sealing means for endy suction centrifugal pumps where the shaft does not extend through the suction eye, used especially where the liquid pumped is corrosive and contains suspended abrasive mattei'.

Considerable trouble has been experienced due to the short life of the packings in present-day stuiiing boxes used for such liquids, the ditiiculty being in partV due to the excessive pressure exerted by the glands to compress the packing, and also due to the greatly increased speeds at which modern pumps are run.

'lhe object of the present invention is to prevent the breakdown of such stuing box packings by providing a seal that is automatically disengaged and rendered' inoperative while its service is not required, thus' greatly` increasing the life of the seal.

Another object isV to provide the single suction impeller with pump-out vanes producing a suction pressure near the seal at least as low as the pressure of the atmosphere, so that during such a condition no shaft seal is required; Thus the result is that in effect only a stationary seal is needed to prevent escape of uid while the pump is standing idle.

A further object is to incorporate means directly or indirectly responsive to the rotation of the impeller to urge to disengage the seal, and meansV responsive to the presence of tiuid near the shaft to urgetoA engage the seal to prevent the escape of fluid. The latter meansmay be a pressure sensitive device responsive to the pressure that exists a predetermined distance from theV shaft; Whereas the means responsive to the rotation' of the impeller'may be a centrifugal device or a pressure responsive means actuated by the hydraulic pressure produced by rotation of the impeller.

The invention alsoaims toA extend the'use of the novel seal to centrifugal pumps operating under a considerable positive suction head, bylengthening the pump-out vanes in relation'with the impeller vanes, or by using two-stage pump-out vanes and/or by introducing air under. pres sure to an enclosed sealing compartment to oppose the fluid which tends to escape'through the automatic shaft seal; another shaft seal being then required, which, however, may be located near the bearings to be thoroughly lubricated and is not in contact with the pumpingliquid.

Other objects and advantages. of this invention'will be apparent from theA following descriptionk considered in connection with the accompanying drawings submitted for the purpose of illustration and not to. dene'the scope of the invention, reference beinghad-for that'purpose-tol the subjoined claims. In the drawings, wherein similar reference characters refer to-similar parts throughoutthe several views: Y

Fig. l is a fragmentary cross-sectional view of' a centrifugal pump showing a stuling boxtarrangementwhere the automatic releasing device-is incorporated;

Fig. 2, a cross-sectional elevation of a modified'form of the invention, thev entire system-being illustrated diagrammatically; p

Fig. 3, a cross-section through the drive shaft looking at the face of seal 76 that is secured to the'shaft shown in F ig. 2;

Fig. 4, a cross-sectional elevation of another'modication; and

Fig. 5, a fragmentary sectional viewsimilar'to'Fig. 4, showing the seal disengaged.

Before explaining the present invention in detail, it is tobe understood that the invention is-.not limitedlin itsl 2,698,584 Patented Jan. 4, 1955 impeller 1u provided with vanes 11 extending trom a back shroud 12 equipped with a plurality of pump-out vanes 13 which should be longer than the impeller vanes in order to produce a greater head so that during operation theV liquid level is a sulhcient distance from the axis of the shaft and all liquid is drawn away from the seal, which will be referred to later. The impeller is secured to an overhuug shaft 14 supported in the conventional manner as with anti-friction bearings 15, of which only one is shown. casing 17 which may be one part with suction head 125. As in most conventional centrifugal pumps the frame is open at 19 to allow access to the shaft seal housed in the hub or casing 2li having a bore 21 in which slides a gland 22 carrying a seal or packing 23 retained by a spring 24 through an intermediate metal ring 25. The seal 23 has a'sealing face in sliding contact with a rotary element 26 axially slidable on shaft 14 and turning therewith as one end engages a splined collar 27 held nrmly between the hub of impeller 16 and shoulder 28 of shaft 14. A spring 29 urges the rotary element in contact with seal 23, the interposed packing 36 serving to prevent leakage between the rotary element and the shaft. Gland 22 and seal 23V are prevented from rotation by a pin 31 extending from casing 2d into aslot 32 cut into Athe outer flange of gland 22. 'the packing 23 also serves to errectively seal against'leakage between the gland and bore 21. The bolts or studs used in conventional pumps for securing the gland here serve to support a seal operating device comprising a body 33 arranged to straddle shaft 14 with a pair of lugs 34 securedto studs 35 extending from frame 1o. The upper part of body 33 has a hydraulic cylinder 36 with a bore 37 in which slides a piston 36 providedV posing it is a low pressure fluid operated device comprisf ing a diaphragm 44 clamped between diaphragm plates 45 mounted on piston rod 40. The outer portion of thel diaphragm is clamped to body 33 by a ring 46, whereby a chamber 47 is formed which is connected through line 4 to a point near the inner ends of the pump-out vanes, to he subject to the suction head produced by the pumpout vanes. Closing'of the seal, or engagement of stationary seal 23 with rotary element 26, is effected by means of a strong conical spring 49 pushing through diaphragm plate 45 and piston rod 40 against forked lever Si? pivoted at 51 on a stud supported'with lugs 34 and pressing against gland 22 at S2. The movement of lever Sil islimited as the shoulder of piston 38 stops againstv end wall 41, whereby element 26 is pushed away from shoulder 53 of collar 54 a short distance and is yieldingly held in contact with packing 23 by virtue of spring 29. Thus a predetermined and even pressure is exerted to keep the seal in contact, the pressure being increased only by an increase in hydraulic pressure of the pumping liquid tending to escape from the pump through the seal.

ln the construction shown in lrig. 2, the invention is incorporated as an integral part of the pump. rille pump comprises a casing 60 having a mounting base 61 and a suction nozzle 62. The volute 63 has the usual discharge nozzle not shown in the section. Within the casing revolves an open impeller 64 having vanes 65 extending from a back shroud 66 provided with pumpout vanes 67. rThe impeller is mounted on a drive shaft 63 revolving in anti-friction bearings 69 supported in a frame or housing 74.) clamped to casing 63 by means of bolts 71, with a shroud or wall 72 interposed having a Ahub 73 with a bore allowing sufficient clearance for shaft 68.- Escape of the pumping liquid from the space between impelier shroud 66 and wall 72 along shaft The support or frame 16 is bolted to tne pumpV into chamber 74 is prevented by a shaft seal comprising a non-revolving sleeve 75 axially slidable on the hub of wall 72 and a rotating sealing disc 76 xed to shaft 68 by means of collar 77 and retaining ring 78, the disc being held tightly on the shaft so that no leakage along the shaft is permitted. To facilitate easy replacement the packing is split into similar halvesand joined in a manner to prevent radial leakage, as shown in Fig. 3 and indicated by numeral 79. rl'he sealing face of sleeve 75 is urged against disc 76 by spring 80, an O ring packing 81 serving to prevent leakage of fluid from the pump into chamber 82.A 83 indicates a filter to prevent the passage of solid matter to the sealing surfaces. Another similar O ring seal 84 between casing 70 and sleeve 75 prevents leakage from chamber 82 to chamber 74. Operation of sleeve 75 to disengage it from seal 76 is provided by a diaphragm plate 85 resting against a shoulder on sleeve 75 but otherwise being free to move axially on the latter. Diaphragm plate S in turn is engaged by a diaphragm 86 sealing off chamber 82 which in under suction pressure generated by the pump-out vane at a level in line with hole 87 serving to communicate the pressure. The location of hole 87 should be somewhatnearer the axis of the pump than the liquid level in the space between shroud 66 and partition 72 when the pump is in operation. Diaphragm Y 86 is'backed up by and bonded to a ring or plate SSin engagement with pistons 89 sliding in diametrically disposed bores 90 parallel with shaft 68, and actuated by tluid in chamber 91 subject to the discharge pressure of the pump transmitted through lines or passages 92 connected to volute 63 or to a space near the outer edges of the pump-out vanes. The space between diaphragm 86 and wall 93 is open to chamber 74 where the pressure may be varied by a regulator 94 to superimpose a higher pressure in chamber 74 whenever the suction head of the pump is increased. This permits the use of the disengaging seal in pumps having a high positive suction head. For this purpose chamber 74 is fully sealed from the atmosphere, access to the seal elements being provided by a removable cover 95 and a rotary shaft seal 96 preventing leakage through the bearings to the atmosphere. The regulator 94 is shown as a separate unit comprising a cylinder or body 97 having a bore 98 in which slides piston 99 whose piston rod 100 is guided in cover 101 which is bolted or otherwise secured to cylinder 97. A groove in piston rod 100y is engaged by a plate or lever 102 pivoted at 103 in a socket formed when the cylinder and housing are bolted together. At an intermediate point lever 102 has a double stud 104 to engage valve balls 105 and 106 urged into a closed position by springs 107 and 108, the latter being retained by a conduit 109 leading through a valve 110 to a source of air pressure 111. The air pressure may be produced by a compressor or any other means that are available. Spring 107 is retained by a cap screw or plug 112 in a space open to the atmosphere through the hole 113. vThe chamber in which plate 102 is housed is in communication with chamber 74 through line 114, the pressure therein also acting on the back of piston 99. The other side of the latter, or chamber 115, is subjected to the suction pressure of the pump through conduit 116 tapping into intake nozzle 62. The pressure sensitive element 99 of regulator 94 thus is responsive to the :suction pressure of the pump to urge valve 106 to admit more air under higher pressure to chamber 74, and it is also responsive to the air pressure in chamber 74 urging valve 105 to open to relieve the pressure. therein. The ends of stud 104 are of such lengths that both balls are seated when the pressures onrboth sides of piston 99 are equal. The function of the regulator is to adjust the pressure in chamber 74 to be equal Vor nearly equal to the suction pressure of the pump. In order to bias piston 99 towards the left so that the air pressure in chamber 74 is never higher than the positive suction pressure of the pump, a conical spring 117 is placed to act on piston rod 100. Drainage of chamlow hub of support 121. The end of shaft 123 that overhangs into the pump casing carries an impeller 125 having vanes 126 extending from a shroud 127 provided with pump-out vanes 128. A pad or shoulder 129 extending from the back of impeller shroud 127 serves to support a pump-out impeller 130 having pump-out vanes 131 and 132 which when the pump is in operationkeep the uid away from the shaft seal 133. The latter is a stationary disc pressed into a recess in the cover. A sleeve 134 engaging the disc revolves with shaft 123 but is adapted to slide axially on it, leakage between shaft and sleeve being prevented by an O ring seal 135, and a spring 136 serving to urge the sleeve into Contact with sealing disc 133. To disengage the rotating sleeve from the stationary discs when the pump is in operation, an elastic ring 137 of rubber or similar material is provided having an oblong section arranged between the inner portion of shroud 130 and a ange 138 extending from sleeve 134. When the impeller is not revolving, the section is as shown in Fig. 4, however, in operation, where the ring revolves with the impeller, a position is assumed which is illustrated in Fig. 5. The centrifugal force acting on the ring urges it to spread in width, since the outer portion is confined by a recess inimpeller 130, the spreading action thus disengaging sleeve 134 from sealing disc 133. It will be noted that the pump-out device is the equivalent of a multi-stage pump, impeller 130 operating in the first stage. To prevent rotation of uid between the shroud of impeller 130 and shroud or partition 122, I provide stationary guide vanes 139 attached to the latter whereby the pressures of the'i'luid at the discharge end of the rst stage and at the intake of the second stage are the same. In order to prevent the trapping of liquid in the space surrounding ring 137 a passage 140 is provided. Since wear of the seal is eliminated so that it may last indefinitely, it is possible to use a more compact design without the space usually allotted to give access ber 74 is obtained through pipe 118 when valve 119 is to the stutling box. This enables a much shorter overhang for the shaft. Any leakage that might occur through the seal may be drained off through hole 141.

Considering now the operation of the embodiment shown in Fig. l, and assuming that the pump is at rest, with a certain static fluid pressure existing in the pump, gland 22 and sealing ring 23 are urged toward the right by virtue of strong spring 49 acting through lever 50 to assume a position where the shoulder of piston rod 40 rests against the bottom of bore 37. Sleeve 26 sliding on shaft 14 is urged by spring 29 into contact with seal 23 to prevent any escape of fluid from the pump along shaft 14 to the atmosphere. Supposing now that the pump is started,whereby the discharge pressure is gradually increased with the rotary acceleration of the pump, the pressure communicated through line 43 acting on piston 42 exerts a certain force tending to release the, pressure on lever 50 and thereby to permit gland 22 and seal 23 to move towards the left to disengage from sleeve 26. However, as long as the fluid level in the space where the pump-out vanes operate is closer to the axis of the pump than the point where line 48 enters, the pressure of the fluid communicated to chamber 47, however slight, acting on the large area of diaphragm 44, opposes the pressure in chamber 42 to prevent movement of piston 38 to the left and disengagement of the sealing elements. As the rotation of impeller 10 accelerates, the fluid level moves farther away from the axis of the pump, the location depending on the discharge pressure produced by the pump, and the speed .of revolution. When the fluid level nears or reaches connection 48 the pressure in chamber 47 becomes suiciently reduced to yield to the hydraulic pressure in chamber 42, whereby spring 49 is compressed andv rod 40 releases the pressure against lever 50 so that spring 24 is permitted to move gland 22 and disc 23 towards the left to follow lever 50. Sleeve 26 tended by spring 29 VVfollows for a short distance until it stops against shoulder 53, so that further mpvement of gland 22 and seal 23 towards the left separates the stationary seal from rotating sleeve-26;

Describing now the operation of the construction shown in Fig. 2, and assuming first that the pump is at rest, the static hydraulic pressure existing in the pump is communicated through passage 87 into chamber 82 acting on diaphragm 86 to urge pistons 89 toward the left, the opposition Yfor the pressure in chambers 91 being negligible due to the small area oiered by pistons 89.

The movement of diaphragm 86 towards the. left allows sleeve 75 to follow by forceA of spring 80, to, press thel sealing face of sleeve 75 against seal 76 to prevent the escape of uid from the pump. If itis assumed that the regulator 94 is in operation, the static pressure from the pump transmitted through line 11,6l would4 urge piston 9 9g'towardsv the right to open valve 106, and to let, air from source 111 into chamber 74, If the pressure in the latter were slightly higher than theA hydraulic pressure in the pump, diaphragm 86 would be forced toward the right to open the sealY and to cause, leakageV from the pump. This condition is, prevented by spring 117 which acts to bias piston 99 toward the left to open chamber 74 to the atmosphere. Therefore as long as the hydraulic pressure in the pump is positive, it is always higher than the air pressure in chamber 74, With` the pump in operation, the fluid between shroud 6,6Y and partition 72 is impelled by pump-out vanes 67 so that the hydraulic fluid is carried away from, shaft 68 by the resulting centrifugal force. As the uid levelY recedes from the central portion to approach or pass passage 87 the pressure in chamber 82 is reduced so that the hydraulic pressure generated by the pump and acting on pistons S9 pushes sleeve 75 out of engagement through the medium of ring S8, diaphragm 8 6, and diaphragm plate 55, aided by the air pressure in chamber 74` acting on diaphragm 35 from the left. Thus the rotating element 75 is disengaged from the stationary seal 75, and the air from chamber 74 is free to communicate with the space between shroud 66 and wall 72 where` the liquid has receded and to enter into chamber 82 through passage 87 so that the pressures in the latter and in chamber 74 are equalized, whereby the seal is then held open only through the effort of pistons 89, receiving no help anymore from the air pressure in chamher 74. Another elect from the communication of the air pressure to act on the liquid level isl to cause it to move farther away from the center until the hydraulic pressure produced by the pump-out vanes balancesv the hydraulic pressure in vortex chamber 63. Since the pump-out vanes are longer than the impeller vanes65, this liquid level may move out a considerable distance, particularly if the pump operates against a low head, but of course it never reaches the outer periphery of shroud o6 where air could leak into vortex chamber 63. The function of regulator 94 is to control the air pressure in chamber 74. An increase in the suction pressure in the intake nozzle of the` pump is communicated through line 116 to chamber 115 to urge piston 99 towards the right, thereby actuating leverA 102 which opens valve tl to admit airA from source 111 into chamber 74 and through the open seal to oppose the liquid impelled by the pump-out vanes so that the level is a safe distance from the center. The air admitted' through valve 1% also immediately acts on piston 99urging it toward the left torclose valve 166 again. lf the suction pressure is reduced, the existing, higher pressure' in chamber 7d also acting onpistonn 99 .to urge. it towards the eft causes valve ESS to be opened torelieve the excess pressure into the atmosphere. It may be noted that a negative suction headcommunicated to chamber '115 could not reducethepressure in chamber 74 below atmospheric pressure. a

The operation of the modified embodiment shown 1n Fig. 4 will now be described. If the pump is at rest, spring 136 holds sleeve 134 against seal 133 so that any leakage of liquid from the pump is prevented. If operation of the pump is started, liquid is impelled by the pump-out vanes to produce a head equal to the head in the vortex chamber of the pump. The liquid between shroud 13u and partition 122 is prevented from circulation with impeller shroud 130 by the ribs or guide vanes 139 so that the pressure generated in the first stage by vanes 131 and 132 is transmitted to the intake of the second stage where the pressure of the liquid impelled by pump-out vanes 12S is further increased to equal the pressure induced by impeller vanes 126 of the pump. Considering the possibility of the trapping of air that might reduce the hydraulic pressure produced by the pump-out vanes, it may be seen that any air at the inner periphery of the partition 122 is free to rise to the space near the outer periphery of impeller 130, and from there rise to the surface of the liquid near the center. As the liquid level moves outwardly with the increase in rotary speed of the pump so that pump-out vanes 132 arev out of; the liquid, the liquid surrounding; ring 137t is. permitted to flow outl 'through passage 140l to, be replacedby air. Since rubber ring 137 revolves withtthe. impeller.` and therefore is subjected to the centrifugal forces which urge it to move away from the center, and. since. its outer periphery is confined, the soft ring becomes widen and. the inside diameter increases, as illustrated: in Fig. 5, thereby pushing sleeve 134 towards the right and away' from the stationary disc 133. Thus the seal is placed4 out of operation where no friction and consequentlyy no. wear occurs. With the two-stage arrangement, the pumpout vanes are capable of producing a. considerable pressure. to oppose the pressureV generated by the. pump. and to. thereby keep the hydraulic uidV away from the; seal soA that an increased positive suctionV head is permissible. If the suction head and consequently the discharge pressure of the pump is increasedexcessively for somereason, and not expected in the normalV operation of thepump, the fluid level would again rise towards thev center soV that liquid would enter passage 140 to immerse ringA 137. The centrifugal force of the liquid actiugonring- 137 would then counterbalance the centrifugal; force of the ring so that it would assume again its normal shape.

shown in Fig. 4, and the seal would be closed by force,

of spring 136. It should be noted that the function` just described is dependent on the specific gravityof the.

pumping medium and ring 137, thus it is desirable, that.

both have the same or nearly the same specific gravity.

While it may be assumed that the drawings, showcentrifugal pumps that may be mounted horizontally, I wish` to make it clear that the invention lends itself ideallyto vertical pumps driven from the top. Dirt orliquid thereby,

drains away from the seal automatically when the pumpout vanes are in operation..

It is apparent that the fluid pressure responsive Vmecha-` nism for opening and closing the sealristhe mainsub-V stance of the invention and may be constructed in variousways without departing from the scope of the invention.

Since it may contain a piston sliding in ay bore, ora. diaphragm piston having a exible diaphragmto produce.

an expansible chamber, such a construction has been termed in the claims as simply a motor mechanisme- Thus the motor;

There are two such motor mechanisms. mechanism energized by the fluid pressure that exists nearv the outer periphery of the pump-out vanes consists` of elements 36, 37, 33, 39, 40 and 42 in Fig. l, and 89, 90

and 91 in Fig. 2. The larger motor mechanism energized:

by the pressure of the iiuid existing near the inner periphery of the pump-out vanes contains elements44, 45, 46 and 47 as shown in Fig. l, and 82, 85, and 86 irrFig. 2.

Having thus described my invention, I claim: l. A centrifugal pump for pumping'liquids, comprising a casing having walls, an impeller inside of said ment relative to said wall, means to bias V said last-men tioned element into sliding engagement with said iirst mentioned rotatable element, said elements being adapted to be disengaged while said pump is running, pump-out vanes on the back of said shroud in said space to impel the liquid between said shroud and said one wall of said casing to evacuate liquid from the proximity of said seal, said seal being adapted to facilitate the passage of air from the atmosphere to replace the evacuated liquid, a motor mechanism energized by the hydraulic pressure generated by said pump-out vanes near their outer periphery and operatively connected with said seal to disengage said elements, and a second and larger motor mechanism energized by the hydraulic pressure existing near the inner periphery of said pump-out vanes and operatively connected to oppose said rst mentioned motor mecha nism to thereby oppose the opening of said shaft seal.

2. A centrifugal pump for pumping liquids comprising a casing having walls, an impeller inside of said casing, a drive shaft extending into said casing to support and drive said impeller, said impeller having a back shroud spaced a short distance from one of said walls, a seal between said shaft and the wall of said casing where said shaft enters, said seal consisting of two elements, one of which is secured to said shaft to rotate therewith and the other is mounted for axial sliding movement relative to said wall, means to bias said last mentioned clement into sliding engagement with said first mentioned rotatable element, said elements being adapted to be disengaged while said pump is running, pump-out vanes on the back of said shroud to impel the liquid in the space between said shroud and said one wall of said casing to evacuate liquid from the proximity of said seal, the latter being adapted to let in air to replace the evacuated liquid, said space being the only passage for the pumping liquid to reach said seal, pressure sensitive means responsive to a higher pressure produced by said pump operatively connected with said seal to urge to open said seal, and second pressure sensitive means responsive tothe fluid pressure in the proximity of said seal arranged to oppose said irst mentioned pressure sensitive means responsive to a higher pressure to thereby oppose the opening of said seal.

3. A centrifugal pump for pumping liquids, comprising a casing having walls, a drive shaft entering said casing, a seal between said shaft and the wall of said casing where said shafts enters, an impeller mounted on said shaft within said casing to be driven by said shaft, said impeller having a back shroud with pump-out vanes in the back thereof to pump liquid away from said seal when in operation, said pump-out vanes being longer than the vanes of said impeller to be capable of producing a higher head than the vanes of said impeller, said seal comprising a non-rotating element mounted for axial sliding movement relative to said wall and a rotaryV element xed to said shaft, said lelements being operatively arranged to be placed in sliding contact with each other or separated to .eliminate friction and wear, a motor mechanism energized by the discharge pressure generated by said pump-out vanes and operatively connected to separate said elements, a second and larger motor mechanism energized by the uid pressure near the intake of said pump-out vanes and operatively connected with said first mentioned motor mechanism to oppose the latter to thereby oppose the separation of said elements, and a spring to bias said elements into contact with each other.

4. Inra centrifugal pump of the character described, having a disengageable shaft seal and pump-out vanes to vkeep the pumping medium away from said seal, in combination, a high pressure cylinder of small crosssectional area connected to receive hydraulic pressure generated by said pump-out vanes, a piston slidable in said high pressure chamber to be acted upon by said hydraulic pressure, means to transmit the movement of said piston to said seal to separate said seal, a low pressure chamber of large area having a sealed piston movable to expand or contract the volume of said chamber, said chamber being connected to be subject to uid pressure near said seal and near the intake portion of said pumpout vanes, said low pressure chamber piston being positioned to oppose said high pressure piston toV prevent disengagement of said shaft seal in response to the pressure communicated, and means to bias said shaft seal into a closed position.

5. The construction as claimed in claim 4, where a plurality of high pressure cylinders are employed.

6. In a centrifugal pump of the character described, having a disengageable shaft seal, pump-out vanes to keep the pumpingmedium away from said seal, and means responsive to higher pressure produced by said pump-out vanes and lower pressure near said shaft seal to disengage said shaft seal, in combination, asealed chamber outside of said shaft seal, means lto force air under pressure into said chamber, and means to regulate said air pressure to be in a pre-determined proportion to the positive suction head of said pump.

7. In a centrifugal pump of the character described, having a disengageable shaft seal, pump-out vanes to keep the Vpumping medium away from said seal, and means responsive to a higher pressure produced by said pump-out vanes and lower pressure near said shaft seal to disengage said shaft seal, in combination, a sealed chamber outside of said shaft seal to separate the latter from the atmosphere, a source of air pressure, a regulator comprising pressure sensitive means responsive to the pressure produced by the positive suction head of said pump and adapted to direct air from said source of air pressure to said chamber, normally closed valve means to relieve the air pressure in said chamber, and means to transmit the pressure existing in said chamber to oppose said pressure sensitive means and to urge to open said valve means to relieve the pressure in said chamber to be in a pre-determined proportion to the positive suction pressure of said pump.

8. A centrifugal pump for pumping liquids, comprising a casing having walls, an impeller inside said casing, a drive shaft extending into said casing to support and drive said impeller, said impeller having a back shroud spaced a short distance from one of said walls, a seal between said shaft and said wall where said shaft enters, said seal comprising an element xed to and rotating with said shaft and a second element mounted for axial sliding movement relative to said wall and biased for sliding engagement with said element fixed to said shaft, pump-out vanes on the back of said shroud to impel the liquid in the space between said shroud and said one wall of said casing to evacuate liquid from the proximity of said seal, a motor mechanism energized by the hydraulic pressure generated by said pump operatively connected with said seal to urge to open said seal by separation of said elements, and a second motor mechanism responsive to the fluid pressure in the proximity of said seal and arranged to oppose said first mentioned motor mechanism to thereby oppose the opening of said seal.

References Cited in the file of this patent UNITED STATES PATENTS 1,122,051 Wohlenberg Dec. 22, 1914 1,932,214 Hornschuch Oct. 24, 1933 1,947,017 McHugh Feb. 13, 1934 1,967,316 Meeker July 24, 1934 2,258,527 Warman Oct. 7, 1941 2,272,454 Wilfley Feb. 10, 1942 FOREIGN PATENTS 535,747 Great Britain Apr. 21, 1941 652,168 Germany Oct. 26, 1937 

